Efficient pitch multiplication process

ABSTRACT

Pitch multiplied and non-pitch multiplied features of an integrated circuit, e.g., features in the array, interface and periphery areas of the integrated circuit, are formed by processing a substrate through a mask. A photoresist layer is patterned to simultaneously define mask elements in the array, interface and periphery areas. The pattern is transferred to an amorphous carbon layer. Spacers are formed on the sidewalls of the patterned amorphous carbon layer. Protective material is deposited and patterned to expose mask elements in the array region and in parts of the interface or periphery areas. Exposed amorphous carbon is removed, leaving free-standing spacers in the array region. The protective material is removed, leaving a pattern of pitch multiplied spacers in the array region and non-pitch multiplied mask elements in the interface and periphery areas. The pattern is transferred to a hard mask layer, through which the substrate is etched.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/198,581 to Fischer et al., EFFICIENT PITCH MULTIPLICATION PROCESS,filed Aug. 4, 2011, which is a divisional of U.S. patent applicationSer. No. 12/687,005 to Fischer et al., EFFICIENT PITCH MULTIPLICATIONPROCESS, filed Jan. 13, 2010 (now U.S. Pat. No. 8,012,674), which is acontinuation of U.S. patent application Ser. No. 11/521,851 to Fischeret al., EFFICIENT PITCH MULTIPLICATION PROCESS, filed Sep. 14, 2006 (nowU.S. Pat. No. 7,666,578).

This application is related to the following: U.S. patent applicationSer. No. 10/934,778 to Abatchev et al., Method for Integrated CircuitFabrication Using Pitch Multiplication, filed Sep. 2, 2004; U.S. patentapplication Ser. No. 10/931,771 to Tran et al., Methods for IncreasedPhoto Alignment Margins, filed Aug. 31, 2004; U.S. patent applicationSer. No. 11/214,544 to Tran et al., Pitch Reduced Patterns Relative ToPhotolithography Features, filed Aug. 29, 2005; U.S. patent applicationSer. No. 11/366,212 to Werner Juengling, Process Flow for VerticalTransistor Arrays, filed Mar. 2, 2006; and U.S. patent application Ser.No. 11/367,020 to Werner Juengling, Masking Process For SimultaneouslyPatterning Separate Regions, filed Mar. 2, 2006. The entireties of eachof these references are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to integrated circuit fabrication and,more particularly, to masking techniques.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency,integrated circuits are continuously being reduced in size. The sizes ofthe constituent features that form the integrated circuits, e.g.,electrical devices and interconnect lines, are also constantly beingdecreased to facilitate this size reduction.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as dynamic random access memories (DRAMs),flash memory, static random access memories (SRAMs), ferroelectric (FE)memories, etc. To take one example, DRAM typically comprises millions ofidentical circuit elements, known as memory cells. A DRAM memory celltypically consists of two electrical devices: a storage capacitor and anaccess field effect transistor. Each memory cell is an addressablelocation that can store one bit (binary digit) of data. A bit can bewritten to a cell through the transistor and can be read by sensingcharge in the capacitor. By decreasing the sizes of the electricaldevices that constitute a memory cell and the sizes of the conductinglines that access the memory cells, the memory devices can be madesmaller. Additionally, storage capacities can be increased by fittingmore memory cells on a given area in the memory devices. Other memorydesigns can integrate access and storage devices or omit access devices(e.g., cross-point MRAM, PCRAM, etc.).

The continual reduction in feature sizes places ever greater demands onthe techniques used to form the features. For example, photolithographyis commonly used to pattern features, such as conductive lines. Theconcept of pitch can be used to describe the sizes of these features.Pitch is defined as the distance between an identical point in twoneighboring features of a repeating pattern. These features aretypically defined by spaces between adjacent features, which spaces aretypically filled by a material, such as an insulator. As a result, pitchcan be viewed as the sum of the width of a feature and of the width ofthe space on one side of the feature separating that feature from aneighboring feature. However, due to factors such as optics and light orradiation wavelength, photolithography techniques each have a minimumpitch below which a particular photolithographic technique cannotreliably form features. Thus, the minimum pitch of a photolithographictechnique is an obstacle to continued feature size reduction.

“Pitch doubling” or “pitch multiplication” is one proposed method forextending the capabilities of photolithographic techniques beyond theirminimum pitch. A pitch multiplication method is illustrated in FIGS.1A-1F and described in U.S. Pat. No. 5,328,810, issued to Lowrey et al.,the entire disclosure of which is incorporated herein by reference. Withreference to FIG. 1A, a pattern of lines 10 is photolithographicallyformed in a photoresist layer, which overlies a layer 20 of anexpendable material, which in turn overlies a substrate 30. As shown inFIG. 1B, the pattern is then transferred using an etch (preferably ananisotropic etch) to the layer 20, thereby forming placeholders, ormandrels, 40. The photoresist lines 10 can be stripped and the mandrels40 can be isotropically etched to increase the distance betweenneighboring mandrels 40, as shown in FIG. 1C. A layer 50 of spacermaterial is subsequently deposited over the mandrels 40, as shown inFIG. 1D. Spacers 60 (FIG. 1E), i.e., the material extending ororiginally formed extending from sidewalls of another material, are thenformed on the sides of the mandrels 40. The spacer formation isaccomplished by preferentially etching the spacer material from thehorizontal surfaces 70 and 80 in a directional spacer etch, as shown inFIG. 1E. The remaining mandrels 40 are then removed, leaving behind onlythe spacers 60, which together act as a mask for patterning, as shown inFIG. 1F. Thus, where a given pitch previously included a patterndefining one mask element and one space, the same width now includes twomask elements and two spaces, with the spaces defined by, e.g., thespacers 60. As a result, the smallest feature size that can be formedwith a photolithographic technique is effectively decreased.

While the pitch is actually halved in the example above, this reductionin pitch is conventionally referred to as pitch “doubling,” or, moregenerally, pitch “multiplication.” Thus, conventionally,“multiplication” of pitch by a certain factor actually involves reducingthe pitch by that factor. The conventional terminology is retainedherein.

Because the layer 50 of spacer material typically has a single thickness90 (see FIGS. 1D and 1E) and because the sizes of the mask elementsformed by the spacers 60 usually correspond to that thickness 90, pitchdoubling typically produces mask elements of only one width. Circuits,however, generally employ features of different sizes. For example,random access memory circuits typically contain arrays of memory cellslocated in one part of the circuits and logic circuits located in theso-called “periphery.” In the arrays, the memory cells are typicallyconnected by conductive lines and, in the periphery, the conductivelines typically contact interconnects in the periphery or landing padsfor connecting arrays to logic. Peripheral features such as peripheralinterconnects and landing pads, however, can be larger than theconductive lines in the array. In addition, electrical devices in theperiphery, including peripheral transistors, can be larger than theelectrical devices in the array. Moreover, even if peripheral featurescan be formed with the same pitch as features in the array, because maskpatterns formed by pitch multiplication may be limited to those that areformed along the sidewalls of patterned photoresist, it is challengingto employ pitch multiplication while achieving the flexibility, e.g.,geometric flexibility, required to define some features.

Accordingly, there is a need for methods of forming features ofdifferent sizes, especially where some features are formed below theminimum pitch of a photolithographic technique, and especially inconjunction with pitch multiplication.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A-1F are schematic, cross-sectional side views of a sequence ofmasking patterns for forming conductive lines, in accordance with aprior art pitch doubling method;

FIG. 2A is a schematic top plan view of a partially formed integratedcircuit, in accordance with preferred embodiments of the invention;

FIG. 2B is a schematic cross-sectional side view of the partially formedintegrated circuit of FIG. 2A, in accordance with preferred embodimentsof the invention;

FIG. 3 is a schematic cross-sectional side view of the partially formedintegrated circuit of FIGS. 2A-2B after forming lines in a photoresistlayer, in accordance with preferred embodiments of the invention;

FIG. 4 is a schematic cross-sectional side view of the partially formedintegrated circuit of FIG. 3 after transferring the pattern in thephotoresist layer to underlying hard mask and temporary layers andremoving the photoresist layer, in accordance with preferred embodimentsof the invention;

FIG. 5 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 4 after performing a trim etch to widenspaces between mask elements, in accordance with preferred embodimentsof the invention;

FIG. 6 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIG. 5 after depositing a layer of a spacermaterial, in accordance with preferred embodiments of the invention;

FIGS. 7A-7B are schematic, cross-sectional side and top plan views ofthe partially formed integrated circuit of FIG. 6 after performing aspacer etch, in accordance with preferred embodiments of the invention;

FIG. 8 is a schematic, cross-sectional side view of the partially formedintegrated circuit of FIGS. 7A-7B after depositing a layer of protectivematerial, in accordance with preferred embodiments of the invention;

FIGS. 9A-9B are schematic, cross-sectional side and top plan views ofthe partially formed integrated circuit of FIG. 8 after patterning theprotective layer to expose mask elements in the array region and otherselected areas of the partially formed integrated circuit, in accordancewith preferred embodiments of the invention;

FIGS. 10A-10B are schematic, cross-sectional side and top plan views ofthe partially formed integrated circuit of FIGS. 9A-9B after removinghard mask and temporary layer material in regions exposed by thepatterned protective layer, thereby leaving a pattern of free-standingspacers, and subsequent removal of the protective layer, in accordancewith preferred embodiments of the invention;

FIG. 11 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIGS. 10A-10B after etching the pattern ofpitch multiplied and non-pitch multiplied mask elements into anunderlying hard mask layer, in accordance with preferred embodiments ofthe invention;

FIG. 12 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 11 after transferring the pattern ofpitch multiplied and non-pitch multiplied mask elements to theunderlying substrate, in accordance with preferred embodiments of theinvention;

FIG. 13 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 12 after removing mask elementsoverlying the substrate, in accordance with other preferred embodimentsof the invention; and

FIG. 14 is a schematic, cross-sectional side view of the partiallyformed integrated circuit of FIG. 12 or 13 after removing all maskelements overlying the substrate, in accordance with other preferredembodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Because of the difference in size between pitch multiplied features andlarger features such as non-pitch multiplied features, connecting pitchmultiplied features to the larger features can be difficult. Forexample, the pitch multiplied features are typically too small and/orclosely spaced to reliably contact features such as contact plugs orlarger sized interconnects. Shorting or other misalignments can occurbecause of the small size and/or close spacing of the pitch multipliedfeatures. Various strategies have been proposed for forming pitchmultiplied and non-pitch multiplied features. Exemplary methods forforming pitch multiplied and non-pitch multiplied features are describedin U.S. patent application Ser. No. 10/934,778 to Abatchev et al. andU.S. patent application Ser. No. 10/931,771 to Tran et al., both ofwhich are assigned to the assignee of the present application. Theentire disclosures of each of these references are incorporated byreference herein.

In addition to difficulties with forming and connecting pitch multipliedand non-pitch multiplied features, the process flows can be complicated,due to the need to form and overlay features of different sizes. Forexample, the pitch multiplied features can be formed separately from thelarger sized features, thereby requiring multiple mask formation andmask consolidation steps. It will be appreciated that each additionalstep in a process flow can undesirably add to the complexity and expenseof a process flow. Moreover, each additional step has the possibility ofintroducing misalignments and etch and pattern transfer complicationsand other errors which can cause undesirable variations in processresults.

In view of these difficulties, preferred embodiments of the inventionallow for the formation and connection of pitch multiplied and non-pitchmultiplied features using an advantageously simple process flow.Preferably, parts of a selectively definable layer (e.g., a photoresistlayer) corresponding to the array, interface and periphery areas of anintegrated circuit are simultaneously patterned. Pitch multiplication isused to form pitch multiplied spacers in the array region. At least someparts of the interface and the periphery regions are protected using aprotective material while other parts are etched and free-standingspacers are formed in the array region. The protective material is thenremoved and a pattern including spacers in the array region and featuresin the interface and the periphery regions are then transferred to ahard mask layer. The hard mask layer can be used to pattern anunderlying substrate.

Advantageously, processing according to the preferred embodiments allowsfor the formation and connection of pitch-multiplied to non-pitchmultiplied features using relatively few process steps. The relativelysmall number of steps can improve the uniformity of process results.Non-uniformities introduced by additional pattern formation and patterntransfer steps can be reduced. Moreover, as discussed herein, becauseconnections of non-pitch multiplied mask elements to pitch multipliedmask elements can be formed simultaneously on the same vertical levelwith the non-pitch multiplied mask elements, defects caused bymisaligning separately formed mask elements can be reduced. Thus,connections to pitch multiplied features can be formed more reliably,thereby reducing the possibility of shorts and poorly connectedpitch-multiplied features. In addition, the relatively low number ofprocess steps advantageously allows for the fabrication of integratedcircuits with high throughput and relatively low cost.

Reference will now be made to the Figures, wherein like numerals referto like parts throughout. It will be appreciated that these Figures arenot necessarily drawn to scale.

Initially, a stack of layers suitable for forming a pattern in a hardmask layer is formed.

With reference to FIG. 2A, a top view of a partially fabricatedintegrated circuit 100 is shown. While the preferred embodiments can beused to form any integrated circuit, they are particularlyadvantageously applied to form devices having arrays of electricaldevices, including memory cell arrays for volatile and non-volatilememory devices such as DRAM, ROM or flash memory, including NAND flashmemory, or integrated circuits having logic or gate arrays. The logicarray can be a field programmable gate array (FPGA) having a core arraysimilar to a memory array and a periphery with supporting logics. As aresult, the integrated circuit 100 can be, e.g., a memory chip or aprocessor, which can include both a logic array and embedded memory, orany other integrated circuit having arrays of features, such as a logicor a gate array.

With continued reference to FIG. 2A, a central region 102, the arrayregion or simply “array,” is surrounded by a interface region 104, whichis surrounded by a peripheral region 106, also referred to as the“periphery.” It will be appreciated that, after fabrication of theintegrated circuit 100 is completed, the array 102 will typically bedensely populated with conducting lines and electrical devices such astransistors and capacitors. In a memory device, the electrical devicesform a plurality of memory cells, which are typically arranged in aregular grid pattern at the intersection of word lines and bit lines.Desirably, pitch multiplication can be used to form features such asrows and/or columns of transistors and capacitors in the array 102, asdiscussed below.

On the other hand, the periphery 106 typically comprises features largerthan those in the array 102. Conventional photolithography, rather thanpitch multiplication, is preferably used to pattern features, such aslogic circuitry, in the periphery 106, because the geometric complexityof logic circuits located in the periphery 106 makes using pitchmultiplication difficult. For example, features in the periphery 106typically do not have the repeating regularity of features typical inthe array 102. Moreover, the logic area need not be as dense as thearray regions 102, such that pitch multiplication in the logic area isunnecessary. In contrast, the regular grid typical of array patterns isconducive to pitch multiplication. In addition, some devices in theperiphery require larger geometries due to electrical constraints,thereby making pitch multiplication less advantageous than conventionalphotolithography for such devices.

The interface region 104 can contain both array and periphery features.For example, the interface region 104 can serve as a transition from thearray 102 to the periphery 106 and allow contact between features in thearray 102 and features in the periphery 106.

While schematically illustrated as concentric regions, it will beappreciated by the skilled artisan that the relative positions, and thenumber of array 102, interface 104 and periphery 106 regions in theintegrated circuit 100 may vary from that depicted. For example, in someareas of the integrated circuit 100, the interface 104 and periphery 106regions may be disposed directly with either side of the array region102, as illustrated in some of the figures below. Moreover, whilecertain specific characteristics of these regions have been noted aboveand clear demarcations between the regions have been illustrated forease of discussion, in some arrangements, two or more of the regions canoverlap.

FIG. 2B shows a cross-sectional side view of the partially formedintegrated circuit 100. Various masking layers 120-150 are preferablyprovided above a substrate 110. The layers 120-150 will be etched toform a mask for patterning the substrate 110, as discussed below.

The materials for the layers 120-150 overlying the substrate 110 arepreferably chosen based upon consideration of the chemistry and processconditions for the various pattern forming and pattern transferringsteps discussed herein. Because the layers between a topmost selectivelydefinable (e.g., photodefinable) layer 120 and the substrate 110preferably function to transfer a pattern derived from the selectivelydefinable layer 120 to the substrate 110, the layers 130-150 between theselectively definable layer 120 and the substrate 110 are preferablychosen so that they can be selectively etched relative to other exposedmaterials. It will be appreciated that a material is consideredselectively, or preferentially, etched when the etch rate for thatmaterial is at least about 2-3 times greater, preferably at least about10 times greater, more preferably at least about 20 times greater and,most preferably, at least about 50 times greater than that forsurrounding materials. Because a goal of the layers 120-140 overlying asecond hard mask layer 150 is to allow well-defined patterns to beformed in the second hard mask layer 150, it will be appreciated thatone or more of the layers 120-140 can be omitted or substituted ifsuitable other materials, chemistries and/or process conditions areused.

In the illustrated embodiment, the selectively definable layer 120overlies a first hard mask, or etch stop, layer 130, which overlies atemporary layer 140, which overlies the second hard mask, or etch stop,layer 150, which overlies the substrate 110 to be processed (e.g.,etched) through a mask. Preferably, the mask through which the substrate110 is processed is formed in the second hard mask layer 150.

With continued reference to FIG. 2B, the selectively definable layer 120is preferably photodefinable, e.g., formed of a photoresist, includingany photoresist known in the art. For example, the photoresist can beany photoresist compatible with 157 nm, 193 nm, 248 nm or 365 nmwavelength systems, 193 nm wavelength immersion systems, extremeultraviolet systems (including 13.7 nm wavelength systems) or electronbeam lithographic systems. In addition, maskless lithography, ormaskless photolithography, can be used to define the photodefinablelayer 120. Examples of preferred photoresist materials include argonfluoride (ArF) sensitive photoresist, i.e., photoresist suitable for usewith an ArF light source, and krypton fluoride (KrF) sensitivephotoresist, i.e., photoresist suitable for use with a KrF light source.ArF photoresists are preferably used with photolithography systemsutilizing relatively short wavelength light, e.g., 193 nm. KrFphotoresists are preferably used with longer wavelength photolithographysystems, such as 248 nm systems. In other embodiments, the layer 120 andany subsequent resist layers can be formed of a resist that can bepatterned by nano-imprint lithography, e.g., by using a mold ormechanical force to pattern the resist.

The material for the first hard mask layer 130 preferably comprises aninorganic material. Exemplary materials include silicon oxide (SiO₂),silicon or a dielectric anti-reflective coating (DARC), such as asilicon-rich silicon oxynitride. In the illustrated embodiment, thefirst hard mask layer 130 is a dielectric anti-reflective coating(DARC). Using DARCs for the first hard mask layer 130 can beparticularly advantageous for forming patterns having pitches near theresolution limits of a photolithographic technique. The DARCs canenhance resolution by minimizing light reflections, thus increasing theprecision with which photolithography can define the edges of a pattern.

The temporary layer 140 is preferably formed of amorphous carbon, whichoffers very high etch selectivity relative to the preferred hard maskmaterials. More preferably, the amorphous carbon is a form of amorphouscarbon that is highly transparent (so-called “transparent carbon”) tolight and that offers improvements for photo-alignment by beingtransparent to the wavelengths of light used for such alignment.Deposition techniques for forming such transparent carbon can be foundin A. Helmbold, D. Meissner, Thin Solid Films, 283 (1996) 196-203, theentire disclosure of which is incorporated herein by reference.

The second hard mask layer 150 can be formed of a hard mask materialsuitable for etching the underlying substrate 110 and which can beselectively etched relative to exposed overlying materials, such asspacers 165 (FIG. 11). For example, in some embodiments where the spacermaterial (FIG. 11) is silicon oxide or silicon, the hard mask materialcan be silicon nitride. In other embodiments where the spacer materialis silicon nitride or silicon, the hard mask material can be siliconoxide. In the illustrated embodiment, the hard mask material is anitride, preferably silicon nitride.

It will be appreciated that the substrate 110 can include a layer of asingle material, a plurality of layers of different materials, a layeror layers having regions of different materials or structures in them,etc. These materials can include semiconductors, insulators, conductors,or combinations thereof. For example, the substrate can comprise dopedpolysilicon, an electrical device active area, a silicide, or a metallayer, such as a tungsten, aluminum or copper layer, or combinationsthereof. In some embodiments, the mask elements discussed below candirectly correspond to the desired placement of conductive features,such as interconnects or landing pads, in the substrate. In theillustrated embodiment, the upper portion of the substrate 110 includesan insulator and the location of mask elements can correspond to thedesired location of insulators, such as in damascene metallization.Examples of structures formed in the substrate include interconnects,gate stacks and shallow trench isolation structures.

The layers 120-150 discussed herein can be formed by various methods.For example, spin-on-coating processes can be used to formphotodefinable layers. Various vapor deposition processes, such aschemical vapor deposition, can be used to form hard mask layers.Preferably, a low temperature chemical vapor deposition (CVD) process isused to deposit the hard mask layers or any other materials, e.g.,spacer material, over the temporary layer 140, especially in cases wherethe temporary layer 140 is formed of amorphous carbon.

The amorphous carbon for the temporary layer 140 can be formed bychemical vapor deposition using a hydrocarbon compound, or mixtures ofsuch compounds, as carbon precursors. Exemplary precursors includepropylene, propyne, propane, butane, butylene, butadiene and acetelyne.A suitable method for forming amorphous carbon layers is described inU.S. Pat. No. 6,573,030 B1, issued to Fairbairn et al. on Jun. 3, 2003,the entire disclosure of which is incorporated herein by reference. Inaddition, the amorphous carbon may be doped. A suitable method forforming doped amorphous carbon is described in U.S. patent applicationSer. No. 10/652,174 to Yin et al., the entire disclosure of which isincorporated herein by reference.

Next, patterns are formed and transferred to the hard mask layer 150.

It will be appreciated that in any of the steps described herein,transferring a pattern from an overlying level to an underlying levelinvolves forming integrated circuit features or mask elements in theunderlying level that generally correspond to mask elements in theoverlying level. For example, the path of lines in the underlying levelwill generally follow the path of lines in the overlying level and thelocation of other elements or features in the underlying level willcorrespond to the location of similar elements or features in theoverlying level. The precise shapes and sizes of elements or featurescan vary from the overlying level to the underlying level, however. Forexample, depending upon etch chemistries and conditions, the sizes ofand relative spacing between the elements or features forming thetransferred pattern can be enlarged or diminished relative to thepattern on the overlying level, while still resembling the same initial“pattern,” as can be seen from the example of shrinking the first resistmask in the embodiments described below. Thus, even with some changes inthe dimensions of elements or features, the transferred pattern is stillconsidered to be the same pattern as the initial pattern. In contrast,forming spacers around mask elements can form new (pitch multiplied)patterns.

With reference to FIG. 3, a pattern comprising spaces or trenches 122,123 which are delimited by array elements 124, interface elements 126and periphery element 128, is formed in the photodefinable layer 120.The elements 124, 126, 128 are formed of photodefinable material. Thetrenches 122, 123 can be formed by, e.g., photolithography with 248 nmor 193 nm light, in which the layer 120 is exposed to radiation througha reticle and then developed. After being developed, the remainingphotodefinable material, photoresist in the illustrated embodiment,forms the illustrated elements 124, 126, 128 (shown in cross-sectiononly). In the illustrated embodiment, the array elements 124 are lines.

The pitch of the lines 124 is equal to the sum of the width of a line124 and the width of a neighboring space 122. To minimize the criticaldimensions of elements formed using this pattern of lines 124 and spaces122, the pitch can be at or near the limits of the photolithographictechnique used to pattern the photodefinable layer 120. For example, forphotolithography utilizing 248 nm light, the pitch of the lines 124 canbe about 100 nm. Thus, the pitch may be at the minimum pitch of thephotolithographic technique and the spacer pattern discussed below canadvantageously have a pitch below the minimum pitch of thephotolithographic technique. Alternatively, because the margin of errorfor position and element size typically increases as the limits of aphotolithographic technique are approached, the lines 124 can be formedhaving larger element sizes, e.g., for a pitch of about 200 nm, tominimize errors in the position and sizes of the lines 124.

With reference to FIG. 4, the pattern in the photodefinable layer 120 istransferred to the hard mask layer 130 and the temporary layer 140 toallow for deposition of a layer 160 of spacer material (FIG. 6). It hasbeen found that the temperatures used for spacer material deposition aretypically too high for photoresist to withstand. Thus, the pattern ispreferably transferred from the photodefinable layer 120 to the firsthard mask layer 130 and the temporary layer 140, which are formed ofmaterials that can withstand the process conditions for spacer materialdeposition and etch, discussed below. In addition to having higher heatresistance than photoresist, the material forming the temporary layer140 is preferably selected such that it can be selectively removedrelative to the material for the spacers 165 (FIG. 10) and for theunderlying second hard mask layer 150. As noted above, the layer 140 ispreferably formed of amorphous carbon and, more preferably, transparentcarbon.

The pattern transfer may be accomplished in a single step; that is, insitu in a single process chamber. The transfer is preferablyaccomplished using anisotropic etches. Preferred etch chemistriesinclude an etch using fluorocarbon plasma, e.g., plasma generated fromHBr/CF₄, to etch the first hard mask layer 130 and an oxygen-containingplasma, e.g., a SO₂/O₂ plasma, to etch the temporary layer 140. Theetches selectively etch the first hard mask layer 130 relative to thephotodefinable layer 120 and then continue through the temporary layer140, stopping at the second hard mask layer 150. Part of thephotodefinable layer 120 may be etched during the pattern transfer. Anyremaining resist forming the photodefinable layer 120 can subsequentlybe separately removed by various processes known by the skilled artisan,including, e.g., by plasma ashing.

With reference to FIGS. 4 and 5, spaces 132, 133 between array elements134, interface elements 136 and periphery elements 138 are preferablywidened by etching the elements 134, 136, 138 to form modified spaces132 a, 133 a and elements 134 a, 136 a, 138 a after a trim etch. Theelements 134, 136, 138 are preferably etched using an isotropic etch to“shrink” those elements. Suitable etches include etches using anoxygen-containing plasma, e.g., a SO₂/O₂/N₂/Ar plasma, a Cl₂/O₂/Heplasma or a HBr/O₂/N₂ plasma. The extent of the etch is preferablyselected so that the widths of the elements 134 a, 136 a, 138 a allowfor the formation of spacers 165 (FIG. 7A) having a desired spacing, aswill be appreciated from the discussion below. For example, the width ofthe elements 134, 136, 138 in the array can be reduced to from about80-120 nm to about 40-70 nm. Advantageously, the width-reducing etch canform lines in the array that are narrower than would otherwise bepossible using the photolithographic technique used to pattern thephotodefinable layer 120. In addition, the etch can smooth the edges ofthe elements 134 a, 136 a, 138 a thus improving the uniformity of thoseelements. While the elements 134 a, 136 a, 138 a can be trimmed to havecritical dimensions below the resolution limits of the photolithographictechnique, it will be appreciated that this trim does not alter thepitch of the spaces 132 a, 133 a and elements 134 a, 136 a, 138 a in thearray, since the distance between identical points in those elementsremains the same. In other embodiments, instead of or in addition toperforming a trim etch on the elements 134, 136, 138, it will beappreciated that the elements 124, 126, 128 (FIG. 3) in thephotodefinable layer 120 can be subjected to a trim etch beforetransferring the pattern from the photodefinable layer 120 to the firsthard mask layer 130, to form elements of desired size in the hard masklayer 130 and temporary layer 140.

With reference to FIG. 6, a layer 160 of spacer material is preferablyblanket deposited conformally over exposed surfaces, including exposedtop surfaces and sidewalls of the hard mask layers 130, 150 and thesidewalls of the temporary layer 140. The spacer material can be anymaterial that can act as a mask for transferring a pattern to theunderlying hard mask layer 150. The spacer material preferably: 1) canbe deposited with good step coverage; 2) can be deposited at atemperature compatible with other materials in the partially fabricatedintegrated circuit 100; and 3) can be selectively and anisotropicallyetched relative to the temporary layer 140 and the first and second hardmask layers 130, 150. Preferred materials include silicon (e.g.,amorphous silicon), silicon oxides and silicon nitrides. In theillustrated embodiment, the spacer material is silicon oxide, whichprovides particular advantages in combination with other selectedmaterials of the masking stack.

Preferred methods for spacer material deposition include chemical vapordeposition and atomic layer deposition. The thickness of the layer 160is preferably determined based upon the desired width of the spacers 165(FIG. 10). For example, in the illustrated embodiment, the layer 160 ispreferably deposited to a thickness of about 20-80 nm and, morepreferably, about 40-60 nm. Preferably, the step coverage is about 80%or greater and, more preferably, about 90% or greater.

With reference to FIG. 7A, the silicon oxide spacer layer 160 issubjected to an anisotropic etch to remove spacer material fromhorizontal surfaces 166 of the partially formed integrated circuit 100.Such an etch, also known as a spacer etch, can be performed on an oxidematerial using a biased fluorocarbon plasma, e.g., containing CF₄/CHF₃,C₄F₈/CH₂F₂ or CHF₃/Ar plasma, or with a purely physical sputter etch(e.g., an Ar sputter etch). The spacer etch defines pairs of spacers 165around mandrels 134 a and elements 136 a, 138 a.

FIG. 7B shows a top plan view of the partially formed integrated circuit100 of FIG. 7A. As can be seen, the mandrels 134 a can have variousshapes, in addition to being the shape of a line. As noted above, in theillustrated embodiment, the upper part of the substrate 110 is aninsulator and the pattern of the spacers 165 correspond to the desiredpattern of insulator to be formed in the substrate 110. Consequently,open space between the spacers 165 preferably corresponds to the desiredplacement of conductors, such as damascene conductive interconnects, inthe substrate 110. For example, any mandrels 134 a which are laterremoved (FIGS. 10A-10B), can have locations corresponding to thelocations of later-formed interconnects. In such cases, some mandrels134 a can have widened portions 137 which can be used to form landingpads for electrically connecting interconnects formed using the mandrels134 a with electrical features on other vertical levels.

With reference to FIG. 8, a protective layer 170 is deposited over thesurface of the partially fabricated integrated circuit 100. Theprotective layer 170 is preferably also selectively definable. As withthe selectively definable layer 120, the protective layer 170 ispreferably photodefinable, e.g., formed of a photoresist, including anyphotoresist known in the art. In addition, in other embodiments, theprotective, photodefinable layer 170 can be formed of a resist suitablefor patterning by nano-imprint lithography.

With reference to FIG. 9A, the photodefinable layer 170 is patternedusing, e.g., the same photolithographic technique used to pattern thephotodefinable layer 120. Preferably, the layer 170 is exposed toradiation through a reticle and then developed to expose elements thearray region 102 of the partially fabricated integrated circuit 100.Thus, some spacers or pairs of spacers 165 are exposed, while some areprotected by the protective layer 170. In addition, some parts of thehard mask layer 130 are exposed, while some parts are protected.

In addition, elements in the interface areas 104 or periphery 106 canalso be patterned, thereby forming, for example, a void 174 in theperiphery. It will be appreciated that while the spacers 165 in thearray 102 preferably have a pitch or element size smaller than theminimum pitch or resolution of the photolithographic technique used informing it, elements patterned in the layer 170 preferably have a pitchor element size equal to or greater than the minimum pitch or resolutionof the photolithographic technique used to form them.

With reference to FIG. 9B, connections 172 to the spaces between thepitch multiplied spacers 165 can be patterned. It will be appreciatedthat the connections 172 can be the ends of larger dimension elements173 such as those used to pattern an interconnect in the periphery 106or interface region 104. The connections 172 can thus connect one ormore mandrels 134 a to a larger mask element 173 and ultimately allowthe formation of a relatively large interconnect connected topitch-multiplied interconnects in the array 102.

It will be appreciated that some elements of the partially fabricatedintegrated circuit 100 remain protected by the layer 170. In such cases,spacers 165 augment the dimensions of these elements, after removal ofthe protective layer 170.

With reference to FIGS. 10A-10B, parts of the first hard mask layer 130and temporary layer 140 which are left exposed or unprotected by theprotective layer 170 are selectively removed, preferably by ananisotropic etch. Advantageously, the unprotected parts of the hard masklayer 130 and the temporary 140 can be removed in a single step; thatis, in situ in a single process chamber. The hard mask layer 130 can beselectively removed using, e.g., a plasma etch containing HBr/CF₄, andthe temporary layer 140 can be selectively removed using, e.g., a SO₂/O₂plasma etch. The protective layer 170 is then removed, e.g., by plasmaashing.

Thus, the mandrels 134 a (FIG. 9A) are removed, leaving free-standing,pitch multiplied spacers 165 in the array region 102. In the illustratedembodiment, the pitch of the spacers 165 and the spaces between thespacers 165 are roughly half that of the photoresist lines 124 andspaces 122 (FIG. 3) originally formed by photolithography. For example,where the photoresist lines 124 had a pitch of about 200 nm, spacers 165having a pitch of about 100 nm or less can be formed. In addition,elements patterned in the periphery 106 or interface region 104 are alsotransferred to the underlying layers, thereby forming, e.g., the void oropening 176 in the hard mask layer 130 and the temporary layer 140.

With reference to FIG. 11, the pattern defined by the spacers 165 andthe remaining parts of the first hard mask layer 130 and the temporarylayer 140 is transferred to the second hard mask layer 150. The transferis preferably accomplished using an anisotropic etch, e.g., an etchusing a fluorocarbon plasma, e.g., a CF₄/O₂/CH₂F₂-containing plasmaetch.

The substrate can subsequently be processed through the mask defined inthe second hard mask layer 150. For example, with reference to FIG. 12,the pattern can be transferred to the substrate 110. With reference toFIG. 13, it will be appreciated that, where the substrate 110 is etched,etching of the substrate 110 can remove the spacers 165 and theremaining parts of the layers 130, 140. Thus, the second hard mask layer150 is used as the primary mask for etching the substrate 110. In otherembodiments, the spacers 165 and the remaining parts of the layers 130,140 can be removed before or after processing of the substrate 110. Withreference to FIG. 14, the hard mask layer 150 can be removed afterprocessing the substrate 110.

Preferably, the substrate 110 is etched using an anisotropic etchselective for the substrate 110 relative to at least the second hardmask layer 150. It will be appreciated that where the substrate 110comprises different materials, e.g., layers of different materials, asuccession of different chemistries, preferably dry-etch chemistries,can be used to successively etch through these different materials, if asingle chemistry is not sufficient to etch all the different materials.The composition of the substrate 110 can depend upon, e.g., theelectrical device to be formed.

It will be appreciated that the pattern formed by the spacers 165 andthen transferred to the second hard mask layer 150 and the substrate 110can define lines, e.g., interconnects for connecting electrical devices.Preferably, the electrical devices are arranged in an array, such as theelectrical devices which form memory cells in the array region of amemory device. The connections 172 (FIG. 9B) can advantageously defineconnections between larger features in the interface or periphery areasof an integrated circuit and pitch multiplied features, such as definedby the element 171, in the array. After the lines are formed, thepartially fabricated integrated circuit 100 can be subjected tosubsequent processing steps, including forming ancillary electricaldevices and electrical interconnects, to form a completed integratedcircuit, e.g., a memory chip.

It will be appreciated that various modifications of the illustratedembodiments are possible. For example, pitch multiplied patternstypically include closed loops, which are formed by spacers that areformed along the wall of a mandrel. Consequently, in non-damasceneprocesses, where the spacers 165, rather the space between the spacers165, are used to form conductive lines, additional processing steps arepreferably used to cut off the ends of these loops, so that each loopforms two individual, non-connected lines. This can be accomplished, forexample, by forming a protective mask around the parts of the lines tobe maintained, while etching away the unprotected ends of the masks. Asuitable method for cutting off the ends of the loops is disclosed inU.S. patent application Ser. No. 10/931,771 to Tran et al., filed Aug.31, 2004, the entire disclosure of which is incorporated be referenceherein. Advantageously, however, by using the spacers 165 to define thelocation of insulating material, rather than conductive material, thestep of cutting off the ends of the spacer loops can be avoided. Forexample, it is unnecessary to cut off the ends of spacers loops wherethe spaces, e.g., the spaces formerly occupied by the mandrels, betweenthe spacers 165 determine the location and shape of interconnects.

Also, in some cases, the spacers 165 can be removed before processingthe substrate 110. Such removal may be beneficial, for example, wherethe spacers 165 are relatively tall and thin. Such spacers may not bestructurally stable and may deform over the course of an etch of the 110substrate, thereby introducing errors in the pattern etched into thesubstrate. As a result, removal of the spacers 165 and any remainingparts of the hard mask layer 130 or temporary layer 140 mayadvantageously stabilize the mask (defined in this example by the lowerhard mask layer 150) through which the substrate 110 is processed.

In addition, the pitch of the spacers 165 can be more than doubled. Forexample, the spacers 165 can be further pitch multiplied by removing themandrels 134 a, forming additional spacers around the spacers 165,removing the spacers 165, then forming another set of spacers around thespacers that were formerly around the spacers 165, and so on. Anexemplary method for further pitch multiplication is discussed in U.S.Pat. No. 5,328,810 to Lowrey et al.

Moreover, the preferred embodiments can be employed multiple timesthroughout an integrated circuit fabrication process to form pitchmultiplied features in a plurality of layers or vertical levels, whichmay be vertically contiguous or non-contiguous and/or verticallyseparated. In such cases, each of the individual levels to be patternedwould constitute a substrate 110 and the various layers 120-170 canformed over the individual level to be patterned. It will also beappreciated that the particular composition and height of the variouslayers 120-170 discussed above can be varied depending upon a particularapplication. For example, the thickness of the layer 150 can be varieddepending upon the identity of the substrate 110, e.g., the chemicalcomposition of the substrate, whether the substrate comprises single ormultiple layers of material, the depth of features to be formed, etc.,and the available etch chemistries. In some cases, one or more layers ofthe layer 120-170 can be omitted or more layers can be added. Forexample, in some cases, the pattern formed in the second hard mask layer150 can be transferred to one or more additional hard mask layers, toprovide a hard mask with increased resistance to etches selective forthe substrate 110.

Also, while “processing” through a mask layer preferably involvesetching underlying material, processing through the mask layers caninvolve subjecting layers underlying the mask layers to anysemiconductor fabrication process. For example, processing can involveion implantation, diffusion doping, depositing, oxidizing (particularlywith use of a hard mask under the polymer mask), nitridizing, etc.through the mask layers and onto underlying layers. In addition, themask layers can be used as a stop or barrier for chemical mechanicalpolishing (CMP) or CMP can be performed on any of the layers to allowfor both planarization and etching of the underlying layers, asdiscussed in U.S. patent application Ser. No. 11/216,477, filed Aug. 31,2005, the entire disclosure of which is incorporated by referenceherein.

It will be appreciated from the description herein that the inventionincludes various aspects. For example, according to one aspect of theinvention, a method is provided for integrated circuit fabrication. Themethod comprises patterning a first photoresist layer to form aphotoresist pattern over a substrate. The photoresist pattern istransferred to a hardmask layer underlying the photoresist layer and atemporary layer underlying the hardmask layer. Spacers are formed onsidewalls of elements in the patterned hardmask and temporary layers. Asecond photoresist layer is deposited over the spacers and the patternedhardmask and temporary layers. The second photoresist layer is patternedto expose some parts of the patterned hardmask and temporary layers andto expose some of the spacers, while leaving photoresist directly overother parts of the patterned hardmask and temporary layers and overothers of the spacers. The exposed parts of the patterned hardmask andtemporary layers are subsequently preferentially removed. The secondphotoresist layer is preferentially removed.

According to another aspect of the invention, a method is provided forforming an integrated circuit. The method comprises patterning aselectively definable layer to simultaneously define array mask elementsin an array region and periphery mask elements in a periphery region ofa partially fabricated integrated circuit. Pitch multiplication issubsequently performed in the array region to form a plurality offree-standing spacers. A pattern defined at least partly by thefree-standing spacers and the periphery mask elements are simultaneouslytransferred to a substrate.

According to yet another aspect of the invention, a method is providedfor fabricating an integrated circuit. The method comprises providing asubstrate with an overlying photoresist layer. The photoresist layer ispatterned using a photolithographic technique, thereby forming aphotoresist pattern comprising photoresist material separated by voids.The photoresist material and voids extend over an array region and aperiphery region of the integrated circuit. The photoresist pattern istransferred to an underlying temporary layer to form a temporary layerpattern. The elements in the temporary layer pattern are subsequentlyshrunk in both the array and the periphery regions. A blanket layer ofspacer material is deposited over the temporary layer elements. Theblanket layer is etched to form spacers at sides of the temporary layerelements.

According to another aspect of the invention, a partially fabricatedintegrated circuit is provided. The partially fabricated integratedcircuit comprises a plurality of mask elements overlying a hard masklayer. The hard mask layer overlies a substrate. Spacers are disposed onsidewalls of the mask elements. A protective layer directly overliessome of the spacers and some of the mask elements. The protective layeralso leaves others of the spacers and others of the mask elementsexposed.

According to yet another aspect of the invention, a partially formedintegrated circuit is provided. The partially formed integrated circuitcomprises a plurality of pairs of spacers over a substrate. Spacersconstituting each pair of spacers are separated by a selectivelyetchable material. A patterned photoresist layer overlies some of thepairs of spacers. Photoresist overlies at least some spacers in aperiphery or interface region of the partially fabricated integratedcircuit, while spacers in an array region of the partially fabricatedintegrated circuit are exposed.

According to another aspect of the invention, a partially formedintegrated circuit is provided. The partially formed integrated circuitcomprises a plurality of pairs of free-standing spacers disposed over anarray region of the partially fabricated integrated circuit. An otherplurality of other pairs of spacers is disposed on the same level as theplurality of pairs of spacers. Spacers constituting each of the otherpairs of spacers are disposed on sidewalls of a temporary materialselectively etchable relative to the other pairs of spacers. Thetemporary material is provided with one or more openings.

In addition to the above disclosure, it will also be appreciated bythose skilled in the art that various omissions, additions andmodifications may be made to the methods and structures described abovewithout departing from the scope of the invention. All suchmodifications and changes are intended to fall within the scope of theinvention, as defined by the appended claims.

We claim:
 1. An integrated circuit, comprising: a plurality of pairs ofspacers over a substrate, wherein spacers constituting each pair ofspacers are separated by a material selectively etchable relative to thespacers; and a patterned photoresist overlying some of the pairs ofspacers, wherein photoresist overlies at least some spacers in aperiphery or interface region of the integrated circuit, and whereinspacers and material separating the spacers in an array region of theintegrated circuit are exposed.
 2. The integrated circuit of claim 1,wherein the selectively etchable material underlies a hard mask, thehard mask disposed between each pair of spacers.
 3. The integratedcircuit of claim 2, wherein portions of the hard mask are exposedthrough openings in the photoresist in a periphery area of theintegrated circuit.
 4. The integrated circuit of claim 2, wherein thephotoresist directly contacts at least some of the spacers and hardmask.
 5. The integrated circuit of claim 1, wherein a separation betweenpairs of spacers in the periphery region is greater than a separationbetween pairs of spacers in the array region.
 6. The integrated circuitof claim 1, wherein at least some of the pairs of spacers define loops.7. The integrated circuit of claim 1, further comprising a hard maskdisposed between the substrate and spacers.
 8. The integrated circuit ofclaim 1, wherein the spacers are formed from a material selected fromthe group consisting of silicon, silicon nitride, and silicon oxide. 9.The integrated circuit of claim 1, wherein the selectively etchablematerial is a carbon-containing material.
 10. The integrated circuit ofclaim 9, wherein the carbon-containing material is amorphous carbon. 11.The integrated circuit of claim 1, wherein the plurality of pairs ofspacers correspond to features of a memory array.
 12. A integratedcircuit, comprising: a plurality of mask elements overlying a hard mask,the hard mask overlying a substrate; spacers disposed on sidewalls ofthe mask elements; and a protective layer directly overlying some of thespacers and some of the mask elements, the protective layer leaving atleast some others of the spacers and at least some others of the maskelements exposed.
 13. The integrated circuit of claim 12, wherein theprotective layer leaves spacers in an array region of the integratedcircuit exposed.
 14. The integrated circuit of claim 13, wherein somesurfaces of the mask elements in a periphery region of the partiallyfabricated integrated circuit are exposed.
 15. The integrated circuit ofclaim 12, wherein the mask elements are disposed in an array and aperiphery region of the integrated circuit.
 16. The integrated circuitof claim 12, wherein the mask elements comprise a hard mask overlying atemporary layer, wherein the hard mask and the temporary layer areselectively etchable relative to the spacers.
 17. The integrated circuitof claim 12, wherein the mask elements are formed of amorphous carbon.18. The integrated circuit of claim 17, wherein the hard mask is formedof a material selected from the group consisting of silicon oxide,silicon or a dielectric anti-reflective coating.
 19. The integratedcircuit of claim 12, wherein the protective layer comprises an organicmaterial.
 20. The integrated circuit of claim 12, wherein the organicmaterial is photoresist.